PHP/4.3.9
contrary to the notes, gzseek() returns -1 if I try to seek past the end of the file.  here is a function that will return the last seekable position, and put the file pointer there.
/** sets the file pointer at the end of the file
 *  and returns the number of bytes in the file.
 */
function gzend($fh)
{
   $d   = 1<<14;
   $eof = $d;
   while ( gzseek($fh, $eof) == 0 ) $eof += $d;
   while ( $d > 1 )
   {
      $d >>= 1;
      $eof += $d * (gzseek($fh, $eof)? -1 : 1);
   }
   return $eof;
}

